The studies proposed in this application are designed to determine the relative importance of three different neurohumoral mechanisms in the daily regulation of arterial pressure and body fluid volumes: the renin-angiotensin system, vasopressin system, and the low and high pressure stretch receptor reflex systems. The experiments differ from those being conducted in many other laboratories in that they are specifically designed to obtain quantitative data concerning the role of each system in both the acute and long-term control of pressure. (1) A series of studies on the renin-angiotensin system are being performed to determine the extent to which factors such as salt intake and the sympathetic nervous system can alter the acute and long-term open-loop feedback gain of the pressure control system. The long-term significance of this system in pressure regulation is being evaluated by studying the effects of prolonged low-dose angiotensin infusions on the pressure sensitivity, the renal-fluid volume system, the aldosterone system, and the baroreceptor reflexes. (2) A number of studies on the vasopressin system are designed to determine the acute open-loop feedback gain of the vasoconstrictor pressure control system and its long-term significance, since recent findings in conscious dogs indicate that the direct pressure activity may contribute to pressure control. (3) The role of the high pressure and low dynamics and in the control of body fluid volumes will be studied under a variety of circumstances. Normal and baroreceptor denervated dogs will be studied using computerized techniques that enable continuous collection and analysis of data. Finally, the quantitative data obtained in all of the studies will be evaluated by computer modeling techniques.